This invention relates to thrusters, which are systems for the lateral propulsion of waterborne vessels. We are concerned with such thrusters that are permanently installed in the vessel (whether as original equipment or post-fitted) and which may be found at the bow or the stern of the vessel, most usually at the bow.
Such thrusters are very well-known and for the most part can be regarded as a ducted fan of which the propulsive duct is mounted transversely through the hull of the vessel so as to open into water at each side of it. There may be a single or a double pump rotor in the duct and it or they may be reversible.
However, as far as we are aware, all such thrusters have penetrated the hull only by the duct containing the pump rotor, and have been constructed in the usual way for a ducted fan, namely with the rotor occupying as far as practicable the complete cross-sectional area of the duct.
In contrast, according to the present invention a thruster for mounting laterally through the hull of a waterborne vessel has propulsive ducts for opening to respective sides of the vessel and an inlet to the inboard end of both of the ducts, the inlet, being at least partially be provided by a tunnel which at least partially surrounds each of the ducts and like them is for opening to each side of the vessel, the tunnel having an internal cross-sectional area greater than that of the ducts.
An axial or mixed flow pump rotor is mounted in each of the ducts and arranged for driving in respectively opposite lateral directions. Preferably drive to both of the rotors comes from a single prime mover to respective unidirectional drives arranged coaxially with the rotors. The prime mover is preferably reversible. Inboard inlets to the propulsive ducts are preferably arranged symmetrically about the drive to the unidirectional drives.
The propulsive ducts may be entirely contained is within the tunnel and may be coaxial with a cylindrical such tunnel or be off centre of it. The tunnel need not necessarily be circular in outline in its internal cross-section; its outboard ends may be faired to conform to where it penetrates the vessel hull.
A preferred prime mover is a reversible electric motor and a preferred transmission format is a synchronous driving belt which drives one or other of the pump rotors by means of unidirectional roller clutches.
The invention includes a waterborne vessel equipped with such a thruster.